Optimal gate operation of a main drainage canal in a flat,low-lying,agricultural area using a tank model

Chiyoda basin is located in Saga Prefecture in Kyushu Island, Japan, and lies next to the tidal compartment of the Chikugo River to which the excess water in the basin is drained away. Chiyoda basin has a total area of about 1,100 ha and is a typical flat and low-lying paddy-cultivated area. The main problem in this basin is the appropriate operation of drainage structures during and after flood events in order to minimize the inundation damages for crop yield and to fulfill the irrigation requirement in the irrigation period. This paper presents a mathematical model of a drainage system in Chiyoda basin for calculating the flood inundation and optimizing the operation of gates in a main drainage canal. First, the algorithm of gate operation was simulated and the drainage model was then evaluated by comparing the simulated water levels with those observed during an actual rainfall event. The results show that the observed and simulated water levels are in good agreement, indicating that the proposed model is applicable for drainage and inundation analyses in flat, low-lying paddy-cultivated areas. Second, the optimization of gate operation was investigated by trial and error method using a stochastic rainfall time series with a return period of 30 years and the tidal conditions of spring and neap tides in the Chikugo River. Comparing a total inundation time, a total inundation area and maximum inundation depth in the paddy tanks at the upstream and the downstream ends, it was concluded that the present operation based on the gate operators’ experience was almost the optimal one, and the sooner start of opening operation and the later start of closing operation within the operationality of check gates were recommended to minimize the inundation damage. The present operation could be able to minimize the total inundation time, the total inundation area and the maximum inundation depths in paddy tanks and to meet fully both the drainage and the irrigation requirements.     

Evaluation of the management practice for controlling herbicide runoff from paddy fields using intermittent and spillover-irrigation schemes

Two water management practices, an intermittent irrigation scheme using automatic irrigation system (AI) and a spillover-irrigation scheme (SI), were compared for the fate and transport of commonly used herbicides, mefenacet (MF) and bensulfuron-methyl (BSM) in experimental paddy plots. Maximum mefenacet concentrations in paddy water were 660 and 540 μg L⁻¹ for AI and SI plot, respectively. The corresponding values for bensulfuron-methyl were 46.0 and 42.0 μg L⁻¹. Dissipation of the herbicides in paddy water appeared to follow the first-order kinetics with half-lives (DT₅₀) of 1.9–4.5 days and DT₉₀ (90% mass dissipation) of 7.8–11.3 days. The AI plot had no surface drainage, hence no herbicide was lost through paddy-water discharge. However, SI plot lost about 38 and 49% of applied mefenacet and bensulfuron-methyl, respectively. The intermittent irrigation scheme using automatic irrigation system with a high drainage gate was recommended to be a best management practice for controlling the herbicide losses from paddy fields. The paddy field managed by spillover-irrigation scheme may cause significant water and herbicide losses depending on the volume of irrigation and precipitation. The water holding period after herbicide application was suggested to be at least 10 days according to the DT₉₀ index.     

Impact of seawater intrusion control on the environment,land use and household incomes in a coastal area

Agricultural production in the coastal wetlands of Asia is often hindered by salinity intrusion caused by tidal fluctuation. This paper reports changes in environmental and socio-economic conditions that followed the phased construction and operation of sluices for controlling seawater intrusion from 1994 –2000 in a coastal area of the Mekong River Delta, Vietnam. Canal water salinity decreased rapidly upstream of sluices, allowing rice cropping intensification and increased rice production in the eastern part of the study area. However, the livelihoods of farmers in the western part were adversely affected due to cessation of supply of brackish water that was needed for brackish-water shrimp farming, while the acid sulphate soils present there posed problems for rice cultivation. The poor farmers and landless people suffered more because the fishery resource that they depended on declined sharply due to reduced salinity and increased acidity in the canal water. The findings confirmed that the environment and resource use in the coastal lands are very sensitive to external intervention. A clear understanding of the socio-economic and environmental impacts of salinity control measures in coastal areas can help planning to enhance farmers' incomes while minimizing negative environmental impacts. Land-use policy formulation, planning and management should adopt a more holistic approach, taking into account the interests of all resource users, especially the poor, instead of focusing on any particular sector.     

Successful factors and activation theory/concept of water users’ organizations - based on the MWMS project in Thailand

This paper analyzes successful factors and develops theory/concept for the activation of the Water Users’ Organizations (WUOs) in the Modernization of Water Management System (MWMS) project in Thailand. The main successful factors are as follows: (1) improvement of irrigation facilities with the farmers’ participation; (2) providing an opportunity for discussions with farmers to enable the adjustment of water allocation through the establishment of an Integrated Water Users’ Group (IWUG) in the early stages of the project; (3) holding monthly meetings of the IWUG; (4) developing, operating, and monitoring the water allocation plan in cooperation with both farmers and government officials. That is to say, initiation of the facilities’ improvement and the establishment of the WUOs were performed concurrently. Moreover, the farmers participated from the beginning of the planning stage to the management stage. The MWMS project contributed to create a system that farmers can acquire and use irrigation water with reliability. Through this system, farmers could have ownership in their facilities, and then they participated in the operation and maintenance spontaneously. The most important thing is to give priority to a joint study process between the farmers and government officials for producing mutual understanding and building a good confidential relationship.     

膜下滴灌灌溉制度对土壤水盐空间分布及玉米产量的影响

灌溉制度对土壤水盐分布具有密切的关系,土壤水盐的分布又直接影响着作物产量。为了正确合理配置和利用水资源,改善试验区生态环境,减小肇州地区土壤含盐量对玉米产量造成的危害,选择肇州县水利科学试验站作为试验地点,试验结合膜下滴灌,设置4个水平的灌溉定额(200、300、400和500 m~3/hm~2),灌水次数分别为2次、3次和4次,测定并分析不同土层深度处土壤含水率、土壤可溶性盐浓度和玉米产量的变化。结果表明,灌溉定额为400 m~3/hm~2、灌水次数为4次时,玉米产量达到最大,且根系部位抑盐效果较好,是肇州地区较为经济合理的灌溉制度。     

Adaptation of landrace and variety germplasm and selection strategies for lucerne in the Mediterranean basin

Lucerne (Medicago sativa L.) can enhance the economic and environmental sustainability of crop-livestock systems in the western Mediterranean basin, but requires improved adaptation to stressful environments because of a predicted shortage of irrigation water and climate change. This study reports on three-year dry matter yields of five landraces from Morocco, Italy and Tunisia and seven varieties from France, Italy, Australia and USA assessed across 10 agricultural environments of Algeria, Tunisia, Morocco and Italy of which four were rainfed, one was continuously irrigated (oasis management), and five were irrigated but adopted a nine-week suspension of irrigation during summer. Our objectives were targeting cultivars to specific environments, and assisting regional breeding programmes in defining adaptation strategies, genetic resources and opportunities for international co-operation. The crop persisted well in all environments, but environment mean yield was strictly associated (P < 0.01) with annual and spring-summer (April–September) water available. Rainfed cropping implied 42% lower yield with 61% less spring-summer water available relative to irrigation with withheld summer water across three sites hosting both managements. All of these sites showed genotype × management interaction (at least P < 0.10). Cross-over genotype × environment (GE) interaction between top-yielding cultivars occurred across the 10 environments. Total number of harvests (range: 9–23), soil salinity as measured by electrical conductivity (range: 0.20–6.0 dS m⁻¹), and average spring-summer water available (range: 102–932 mm) were selected as significant (P < 0.05) environmental covariates in a factorial regression model explaining 53% of GE interaction variation. This model was exploited for targeting cultivars as a function of site-specific levels of these factors. Its indications agreed largely with those of an additive main effects and multiplicative interaction model with two GE interaction principal components. An Italian landrace exhibited specific adaptation to severely drought-prone environments, whereas landraces from north Africa were not adapted to such environments. One Moroccan landrace was specifically adapted to high number of harvests (partly reflecting frequent mowing). One variety selected for salt tolerance, and one Moroccan landrace, were specifically adapted to salt-stress environments. Environment classification as a function of GE interaction effects indicated three groups which may be object of specific breeding: (i) rainfed or irrigated environments featuring limited spring-summer water available (<350 mm), nil or low soil salinity, and moderate to low number of harvests; (ii) salt-stress environments; and (iii) environments characterized by high number of harvests.     

Evaluation of pollutant removal in a constructed irrigation pond

A year-long study on the water quality and hydrology was carried out to investigate the characteristics of the pollutant concentrations and pollutant removal in a constructed irrigation pond. The pond is part of a circular irrigation system for paddy fields within Lake Kasumigaura watershed, Japan. The average concentrations of the total nitrogen (TN), chemical oxygen demand (COD), total phosphorus (TP), and suspended solids (SS) at the pond outlet were 7.4, 8.6, 0.2, and 18.8 mg L⁻¹, respectively. The average removed loads for the same indices were 0.14, 2.47, 0.11, and 24.2 g m⁻² day⁻¹, respectively. The percentages of pollutant removals from the inflow loads for the same indices were 3, 26, 42, and 63%, respectively. The pond discharged the TN loads of 128 kg due to sediments stirred by operation of a pump for April and May. The average TN removal was 19% from June to August and was smaller than that reported in published literatures (40–50%). Major reasons were considered to be that the turnover of water in the pond was rapid (86% per day) and that the TN concentration of inflow water was relatively low (5.9 mg L⁻¹). The percentages of pollutants that flowed into the pond to the outflow loads from the study site were 6.6, 4.8, 1.6, and 1.1% for TN, COD, TP, and SS loads, respectively. The pollutant removal will be increased if the design of the circular irrigation system is reconsidered to utilize a pollutant removal function in the irrigation pond.     

Long-term changes in nitrogen loads of a stream in the vicinity of an earthen waste storage pond

It is not sufficiently known for how long earthen waste storage ponds that are no more in use continue to affect surface water quality. In 2006, we carried out an investigation on the water quality and hydrology at the outlet of a small agricultural catchment area (area A) by estimating the in-stream nitrogen loads and nitrogen inputs. In this area, swine waste had been retained in an earthen waste storage pond, which was not in use since 1990. Similar investigations were conducted at the same location in 1992 and 2002, and the results of all these three studies were compared. The average nitrate nitrogen (NO₃-N) concentrations were 26, 4.9, and 4.0 mg L⁻¹ in 1992, 2002, and 2006, respectively. Despite 76% of the land use of area A being forest, the average NO₃-N concentration was relatively high, indicating that effluents from the earthen waste storage pond continued to affect surface water quality in 2006. The ranges of in-stream nitrogen loads derived from the earthen waste storage pond were estimated to be 154 to 207, −14 to 39, and 14 to 74 kg ha⁻¹ for 1992, 2002, and 2006, respectively. The results suggested that although the effects of effluents from the earthen waste storage pond on water quality decreased over 14 years, they still continued in 2006.     

Growth, gas exchange, water relations, and ion composition of Phaseolus species grown under saline conditions

We examined the effects of salinity on four wild (Phaseolus angustissimus, Phaseolus filiformis, P. microcarpus, and P. vulgaris) and two cultivated (P. acutifolius and P. vulgaris L.) Phaseolus species. Relative growth rate (RGR, g g⁻¹ per day), unit leaf rate (ULR, g m⁻² per day), leaf area ratio (LAR, m² g⁻¹), specific leaf area (SLA, m² g⁻¹), leaf weight ratio (LWR, g leaf g⁻¹), and rate of ion uptake were calculated for the period between 10 and 20 days after planting. Salinity significantly reduced RGR, ULR, LAR, and SLA whereas LWR showed no definite trend. In all species, except in P. filiformis, ULR, but not LAR, was significantly correlated with RGR, indicating that ULR was an important factor underlying the salinity-induced differences in RGR among species. In P. filiformis, high salinity reduced SLA, and consequently LAR. The significant correlation of SLA and LAR with RGR suggested that growth components affecting leaf area expansion were the primary factors explaining the inhibition of growth in this species. Increasing salinity progressively decreased leaf water vapor conductance. The rate of CO₂ assimilation decreased gradually with salinity, showing significant reductions only at the highest salt level (80 mM NaCl). Approximately two-thirds of the reduction in CO₂ assimilation rate at high salinity was attributable to reduced stomatal conductance. In P. filiformis, however, neither stomatal conductance nor CO₂ assimilation were affected by salt stress. Leaf water and osmotic potentials declined significantly as stress intensified. However, osmotic adjustment permitted the maintenance of positive turgor throughout the growth period. Salinity had a significant effect on tissue concentrations of Na⁺, K⁺, Ca²⁺, and Cl⁻ and on the uptake rate of Na⁺, K⁺, Ca²⁺, and Cl⁻. Thus, in addition to the toxic effects of high concentrations of Na⁺ and Cl⁻ in plant tissue, saline-induced changes in mineral nutrient uptake likely contributed to the reduction of plant growth. It appears that salt tolerance in P. filiformis is associated with Na⁺ exclusion and organ Na⁺ compartmentation in roots and stems as well as sustained K⁺ concentration in leaves and better stomatal control through osmotic adjustment. All other Phaseolus species are Na⁺ excluders, and maintained turgor-driven extension growth by accumulating Cl⁻ (osmotic adjustment), but subsequent weight gain reductions suggest that this led to ion toxicity.     

The Selective Extraction of Glucuronoarabinoxylans from Sorghum Endosperm Cell Walls using Barium and Potassium Hydroxide Solutions

Various populations of hemicellulosic material were solubilised from water-unextractable cell wall material (WUS) of sorghum (Sorghum vulgarecv. Fara Fara) by sequential extractions with alkali. Saturated Ba(OH)₂-solutions, followed by distilled water, 1 KOH, 4 KOH and 4 KOH containing 4% (w/v) H₃BO₃ were used to extract primarily glucuronoarabinoxylans (GAX) from sorghum WUS. Cellulose remained in the residue. In total over 90% of all GAX originally present in the WUS were recovered, particularly in the saturated Ba(OH)₂, 1 KOH and 4 KOH extracts. Saturated Ba(OH)₂ was found to be the most selective of the extractants tested for GAX. (1→3), (1→4)-β- -glucans were found predominantly in the fraction obtained by washing with water after the extraction with saturated Ba(OH)₂. All extracted arabinoxylans were highly substituted (arabinose/xylose>1) and contained, besides -arabinose and -xylose, the acidic sugars -glucuronic, 4-O-methyl- -glucuronic and -galacturonic acid. The average molecular weight ranged from 210 000–1 300 000, which corresponds with DPs ofc. 1500 to 9300. The selectivity of the extractant was apparently enhanced by the presence of a bivalent cation.     

花后水分亏缺对夏玉米产量及水分利用效率的影响

以郑单958为试验材料,分别于吐丝至吐丝15 d、吐丝至吐丝30 d和吐丝30 d至成熟期3个时期进行水分亏缺处理(T1、T2、T3),以花后适宜水分供应为对照(CK),研究花后不同时期水分亏缺对夏玉米产量和水分利用效率的影响。结果表明,3个阶段的水分亏缺均使玉米产量降低,其中,T1处理的降幅最大,T3处理的降幅最小,与CK相比均达到显著性差异。T1处理下玉米的叶片衰老最快,在整个生育后期叶面积指数一直处于较低的水平;成熟期时,各处理的叶面积指数均低于CK。T1和T2处理使成熟期时的单株总干重显著下降,较CK分别下降了24.98%、29.94%。T3处理下作物的水分利用效率最高,比CK高0.5 kg/(mm·hm2);T1处理下作物的水分利用效率最低,且与CK达到显著差异。各个时期的水分胁迫均使玉米的穗粒数减少,穗长变短,穗粗降低,行粒数减少,秃尖变长,空秆率上升。     

Properties of maize starch modified by ball milling in ethanol medium and low field NMR determination of the water molecular mobility in their gels

Ethanol as moisturizing agent and ball-milling treatment, has been combined in order to determine their impacts on the improvement of the properties of physically modified maize (Zea mays) starch granules. The content of ethanol has been set respecting a ratio of starch to ethanol varying from 1:0 to 1:3 (w:v), and the ball-milling time varied between 0 and 72 h. We observed that the increase of the amylose content varied in a more effective way with increase of the milling time (p < 0.05) than with the variation of the starch to ethanol ratios. As expected, modified starches were more transparent, more soluble, less crystalline, and presented damaged structures. In all cases, the starch granule sizes were better distributed at ratios of starch to ethanol of 1:0 and 1:3 (w:v) respectively. In addition, the impact of the combination of these treatments on the mobility of water molecules in starch gels characterized by the transverse relaxation time (T₂), as well as the abundance of protons (¹H T₂) in each populations were determined by low field NMR. Mobility of water molecules within starch gels increased at high temperature. Nonetheless, the proton population at T₂ > 10 ms (characterized by T₂₂) for the modified starch (starch/ethanol, 1:3 w:v) was fundamental in the different water concentrations, and accounts for 70 to 90% of total protons, at temperatures >60 °C.     

Analysis of water management structures of an Integrated Water User Group in the Chao Phraya Delta, Thailand

An Integrated Water User Group (IWUG) plays an important role assisting an irrigation project to control water distribution, expand the cropping area, operate and maintain irrigation facilities, and disseminate crucial information about the water situation to all farmers based on water supply from an irrigation agency. In this article, we present our analysis of the management of a newly established IWUG, based on a field survey in Thailand. We attempt to clarify the characteristics of irrigation management in the IWUG, while focusing on four functional processes: decision, operation, monitoring, and feedback. Thus, we analyze the water management structure and provide suggestions for better management of the IWUG. The main results of our analysis are as follows: (1) the current state of the IWUG 18R canal is not fully successful. There are second generation problems that need to be solved; (2) The upstream farmers dominate the use of the IWUG 18R canal because the establishment process of downstream WUGs was loosely performed because of a limited budget for on-farm irrigation development; (3) Water distribution structure and membership charging are not simple and uniform along the lateral irrigation canal because of the water availability of return flow from the downstream area. Such structure should be recognized and discussed to improve the future water distribution in relation to membership fees.     

Revegetation of barren lakeside land through growth enhancement of Xanthium italicum by rhizobacteria

This study aims to propose a methodology for establishing the optimal rule curves of reservoir operation based on a multi-use reservoir system. Located on the upper Saigon River, Dau Tieng Reservoir plays an important role in economic and social aspects: (1) flood control; (2) domestic and industrial demands; (3) flushing out salt water intrusion from the downstream area; and (4) agriculture irrigation. We propose a reservoir operation model using a constrained genetic algorithm (CGA), in which the fitness function was constrained by penalty functions. The proposed model was formulated by including various water demands configured into the objective function. The penalty functions were designed for various constraints and integrated into the objectives of the operation process to perform the fitness function. The model’s performance was simulated for the last 20 years with 1-month intervals and evaluated through a generalized shortage index (GSI). The derived results of three CGA cases with associated environmental flow requirements significantly improved the efficiency and effectiveness of water supply capability to various water demands as compared to current operation. Among the three cases, CGA case 3 achieved much better water releases from the reservoir as indicated by a small derived GSI value (0.33), the smallest shortage of environmental water (0.11 m³/s) and the highest water usage (63.8 %). Thus, the derived results of CGA case 3 were presented as the best rule curves for reservoir operation. To summarize, CGA was demonstrated as an effective and powerful tool for optimal strategy searching for multi-use reservoir operations.     

Frequency of occurrence of various drought types and its impact on performance of photoperiod-sensitive and insensitive rice genotypes in rainfed lowland conditions in Cambodia

Lowland rice production in the Mekong region is generally low because crops are cultivated under rainfed conditions and often exposed to drought. To examine how field water availability affects productivity of different genotypes in rainfed lowland rice, the field experiments were carried out for six years at eight locations in Cambodia. We classified 34 genotypes used in the experiments into photoperiod-insensitive [short (IS) and medium (IM) maturity] and sensitive [medium (SM) and long-duration (SL) maturity] genotype groups. Mean days-to-flower from sowing was 87 in IS, 112 in IM, 112 in SM and 132 in SL and mean grain yield was 2.0, 2.8, 2.5 and 2.4 t ha⁻¹, respectively. Drought environment was quantified for each experiment by determining whether free water level was observed to be less than the soil surface during three growth stages: GS1 (maximum tillering), GS2 (panicle development) and GS3 (grain filling). The drought frequency estimated from 44 field experiments was 18% in all IM, SM and SL at GS1, 23%, 25% and 32% in IM, SM and SL, respectively at GS2, and 43%, 45% and 57% at GS3. Thus, the drought occurred more frequently after flowering, particularly in the SL group. Based on the results, the IM genotypes may be grown to escape from drought during the GS2 and GS3 periods by sowing early (June) in the drought environment. When sown late (August), the SM genotypes are exposed to less drought risk because they flower earlier than the IM genotypes. Compared with the SM genotypes, the SL genotypes are highly exposed to water stress during the GS3 period, resulting in yield reduction. SM and IM had similar occurrence of drought environment, but yield reduction due to drought was less in SM than in IM. Thus, photoperiod-sensitive cultivars with medium maturity are preferred in drought-prone lowland fields, particularly when sowing is delayed. In the favourable water environment, the SM genotypes can be better than the IM genotypes when sown early in the season, while the IM genotypes performs better than the SM genotypes with late sowing. This suggests that for lowland fields without drought photoperiod-insensitive cultivars are recommended and photoperiod-sensitive cultivars can be preferred if sown early.     

Water-deficit and high temperature affected water use efficiency and arabinoxylan concentration in spring wheat

This study was conducted in a controlled environment to evaluate the combined effects of water-deficit (imposed at the stem elongation stage) and high temperature (imposed at the booting stage) on the water use efficiency (WUE) and arabinoxylan concentration of two spring wheat varieties (‘Superb’ and ‘AC Crystal’) commonly grown in Canada. The temperature treatments were 22/12 (day/night, T1) and 32/22 °C (T2). Overall, time to maturity under high temperature was 10 days shorter for ‘Superb’ than for ‘AC Crystal’, indicating that ‘Superb’ was more sensitive to high temperature stress. Leaf relative water content (RWC) and specific leaf area (SLA) were more sensitive to drought than to high temperature for both varieties. Drought and high temperature decreased (P < 0.05) biomass, water use and grain yield but increased WUE of ’Superb’ and ‘AC Crystal’. Without temperature stress, significant drought and variety effects were found on CID (carbon isotope discrimination) which was negatively correlated with WUE. All gas exchange parameters declined under drought and high temperature. High temperature increased the grain arabinoxylan concentration (especially the water-extractable arabinoxylans). The different arabinoxylan fractions were positively correlated with WUE suggesting that arabinoxylans can be increased by selecting for increased WUE.     

茶皂素鱼毒活性及其应用的研究——Ⅳ.盐度、水温对茶皂素鱼毒活性的影响

以纹缟鰕虎鱼和鲫鱼为材料,对茶皂素的鱼毒活性与水域的盐度、温度的关系进行了研究。结果表明,在海水中茶皂素的毒鱼效果随着盐度升高而增强,当盐度为6.5‰、14.4‰、20.9‰、27.5‰与32.7‰时,茶皂素对纹缟鰕虎鱼的全致死浓度分别为1.0、0.9、0.9、0.7和0.3ppm,表明在盐度高的水域内茶皂素的鱼毒效果更佳。鲫鱼的死亡速度则与盐度呈抛物线关系,即盐度在4‰—10‰时,特别在6‰左右时,茶皂素对鲫鱼的致死速度比较缓慢,低于或高于这一盐度时,死亡加快。上述两种鱼的致死速度还随水温的提高而加速。     

Assessment of changes in water cycles on food production and alternative policy scenarios

This special issue deals with water and food as it applies to water resources and rice production in the Mekong River Basin. The range of papers reflects not only the broad interest but also the complexity of the topic. These reports are mainly based on the research carried out by the project, “Assessment of the Impact of Global-Scale Change in Water Cycles on Food Production and Alternative Policy Scenarios”. Hence the special issue gives a brief overview of the structure, goals, outcomes, and future direction of the above project. What we do in this paper are: (1) giving an overview of the project’s structure and goals, (2) stating the five common outcomes and several more specific results, and (3) looking forward to the future direction of the project. The aim of our research is to draw up scenarios for optimum water-resource distribution and to develop social guidelines, measures, and policies to help solving food and environmental problems by developing a world water–food model that emphasizes rice production in Monsoon Asia. We have integrated all of the data gathered and the research results into a food supply and demand model combined with a water-cycle analysis. We included operational factors, such as water-cycle change, water demand, water supply, and water distribution in the model. Emphasis is placed on the use of efficient resource-management technologies for proper use of water resources in agricultural and other sectors. The water–food model has been developed as a tool for evaluating technical decisions derived under various policy scenarios.     

Productivity Enhancement in the Salt-Affected Lands of Joint Satiana Pilot Project Area of Pakistan

SUMMARY

Salt-affected lands are common in Pakistan and cover an area of 6.8 million ha; i.e., about one-third of the total cultivated area. Reduction in yield of different crops due to salinity and waterlogging is sometimes more than 60%, and annual losses under rice-wheat rotation have been calculated at Rs. 10 billion (US$ 166 million). Other adverse effects of salinity on the community are very large and about 16 million people are affected directly by the hazards of salinity and waterlogging. Average farmers in Satiana project area (38 villages) have 4–5 ha of land, of which approximately 55% are salt-affected. This area is equipped with a modern tile drainage system but it has not shown the expected impact on the rehabilitation of salt-affected soils. Farmers of Satiana area are poor and depend on off-farm activities for their livelihood. Nevertheless, they are keen to improve their soils. A productivity enhancement program was launched in the affected area, where saline agriculture was successfully demonstrated to restore the productivity of salt-affected lands and about 405 ha were successfully rehabilitated by planting salt-tolerant trees, forage shrubs, crops and applying gypsum to improve the soil conditions. Some relevant research studies used to develop the saline agriculture strategy have also been discussed.     

Rice yield modeling under salinity and water stress conditions using an appropriate macroscopic root water uptake equation

The objectives of this study were to evaluate the application of different macroscopic root water extraction models for prediction of rice grain yield based on data obtained in a greenhouse experiment. In this experiment, the irrigation treatments were continuous flooding (control), intermittent flooding (1- and 2-day intervals) and the salinity levels of irrigation water were 0.6 (control), 1.5, 3, 4.5 and 6 dS m(-1) in the year of 2005 and 0.6 (control), 1.5, 2.5, 3.5 and 4.5 dS m(-1) in the year of 2006. A local cultivar (Ghasrodashty/Komphiroozy) was planted in pots under greenhouse condition during years 2005 and 2006. Grain yield and evapotranspiration at different treatments were determined. The effect of salinity and water stress on root-water uptake coefficient was determined by FAO and Homaee and Feddes methods and grain yield was predicted by production functions. The FAO method did not predict the interaction effects of salinity and water stress on reduction of water uptake coefficient especially at high salinity levels, while the Homaee and Feddes method predicted properly the effects of salinity and water stress on root-water uptake coefficient. Further, yield was predicted by using the root-water uptake coefficient suggested by FAO and Homaee and Feddes methods. The results indicated that the FAO method did not predict the yield properly especially in continuous flooding and salinity level of more than threshold values, but the Homaee and Feddes method predicted the grain yield with minimum error.